The present invention relates to an ultrasonic motor and an electronic apparatus employing the ultrasonic motor for friction-driving a moving member by way of vibrating waves produced by utilizing the stretching movement of a piezoelectric element.
Conventionally, such an ultrasonic motor is known that a predetermined high frequency voltage is applied to the piezoelectric element fixed on the vibrating member to produce traveling waves, and the moving member attached in contact with the vibrating member under predetermined pressure is driven by the traveling waves.
Such a conventional structure is disclosed in, for instance, Japanese Laid-open patent application No. 58-148682.
Also, in FIG. 18, there is shown a cross-sectional view of a conventional analog type electronic timepiece. A stator 53 is arranged on the upper plane of the ground plate 40, and a magnetic core 52 is positioned in contact with the upper plane of this stator 53 and then is screwed thereon. A coil wire 51a is wound on the magnetic core 52 and is connected to a driving control circuit (not shown).
A rotor 54 is rotatably associated with a rotor hole 53a of the stator 53. The rotation of the rotor 54 is transported to a fifth wheel 55, a fourth wheel 44, a third wheel 43, a minute wheel 42, a rear wheel of data (not shown), and an hour wheel 45.
When a predetermined voltage is applied in a constant time period to a coil wire 51a, the rotor 54 is rotated by way of magnetic force of the stator 53, so that "hour" is displayed by the hour hand mounted on the hour wheel 45, "minute" is displayed by a minute hand 33 mounted on the minute wheel, and "second" is displayed by a second hand 34 mounted on the fourth wheel.
However, in case of the conventional traveling wave type ultrasonic motor, since two high frequency voltages having the different phases are inputted to the vibrating member so as to rotationally move the moving member, to thereby produce the traveling waves, two sets of the boosting circuit and the driving circuit are required.
Also, since the vibrating characteristics of the vibrating member and the piezoelectric element are changed in response to changes in the temperatures and the driving voltages, such a complex frequency following circuit is needed that the voltage, current, phase and the like applied to the motor are continuously sensitive to changes in the environments. As a consequence, although the structure of the ultrasonic motor is made simple, the driving circuits becomes very complex, whereby there is a problem that the conventional ultrasonic motor may be applied with difficulty to electronic apparatuses.